Various forms of liquid fan spray generation systems are known. By way of example only, one exemplary system is disclosed in U.S. Pat. No. 4,645,126 (incorporated by reference). In such a fluidic oscillation system, a fluid such as a mixture of water and antifreeze is delivered from a power nozzle across an interaction chamber and then through an outlet throat for impingement against the windshield. At the initiation of flow, a power stream of the fluid mixture passes substantially directly across the interaction chamber. As flow progresses and the interaction chamber is filled, vortices are formed on either side of the power stream. As one vortex becomes dominant, the power stream is diverted against the opposite wall and oscillation begins so as to develop a fan spray.
In cold weather conditions, the surface tension and viscosity of the fluid delivered to a nozzle will increase. In those conditions, the fluid may be too thick in character to create velocity in the control channels of the spray system. Thus, in cold weather conditions, the fluid may take the path of least resistance and move straight through the interaction chamber. Under those circumstances, a desired fan spray does not develop.
One approach to address the problem of increased viscosity under cold weather conditions is to increase the pump pressure to promote oscillation. That is, the fluid is delivered to the spray device at a higher pressure. However, the ability to increase pump pressure is necessarily limited and may not be successful in producing, a full fan angle. Moreover, under cold weather conditions, the fluid characteristics of increased surface tension and viscosity will necessarily tend to reduce the fluid delivery pressure for the same energy input. Accordingly, a need exists for a spray device which promotes desirable fan spray characteristics at low temperature conditions without the need to substantially increase pump pressure to the device.